A native device may include NMOS transistors which can be formed without threshold adjusting dopants in the channel region as found in conventional MOS transistors. For example, a native NMOS transistor may be fabricated without PWELL and VTN implants typically utilized in a conventional NMOS device. This elimination of the threshold adjusting dopants can improve the mobility of charge carriers within the channel. Increased mobility can reduce the threshold voltage (VT) and body effect, and further increase the transconductance (gm) of a device, which may be beneficial for analog and mixed signal applications.
Conventional native devices typically also include pocket implants (also called as halo implants) to control the short channel effect. However, with shrinking device dimensions and the usage of heavier pocket implants, the channel mobility of the native device is being reduced. Accordingly, it is becoming increasingly difficult to achieve a low VT and a high gm using native fabrication. Moreover, this reduced mobility may also increase the variations of the characteristics between adjacent devices. In summary, the heavy doping of the pocket implants can contravene the original purpose for using the native fabrication approach.
Accordingly, there is a need for fabrication techniques for native devices that can reduce the dopant concentration within the device channel to maintain low threshold voltages, high transconductance, and improved consistency among fabricated devices.